A motor Vehicle radio is known from DE-0S (German Preliminary Patent) 2,547,659, which has a control device for controlling the volume, where the said control device delivers control voltages, as a function of a signal representing the noise level in the vehicle, to the output stage of the radio. Here a signal dependent on the speed of the vehicle, e.g. the r.p.m. of the engine or the r.p.m. of the drive shaft, is used as the signal representing the noise level.
This known motor vehicle radio has the disadvantage that its sound volume can be controlled only as a function of the speed of the vehicle. Here changes in noise level which are independent of the speed, for example those due to differences in the tires, especially during winter operation, and to travel in rainy weather, are not taken into consideration, nor are individual hearing problems of the user.
Now in order to be able to adapt the sound volume of a motor vehicle radio to such speed-independent changes in noise level, a motor vehicle radio has already been provided according to DE-OS 2,646,232, which has a volume adjustment which depends on the noise level. In this known radio, a noise-detecting measuring probe or a microphone is necessary, whose output signal acts through a deep-pass filter on a control circuit, which then raises or lowers the sound volume of the radio as a function of this signal which characterizes the noises in the surroundings.
Apart from the fact that it is not possible, even in this radio, to adjust individually to hearing problems of the user, a relatively expensive measuring probe, with the appropriate circuitry, is required.
In contrast, the object of the invention is to provide a motor vehicle radio appropriate to the requirements, in which the automatic control of the sound volume can be adjusted optimally to the vehicle and user specific circumstances.
This object is achieved, in accordance with the invention, by having a two-position switch for selectively applying the volume signal of the automatic volume control device or of the manual volume-settinq device to an output stage of the radio which feeds the loudspeakers, and has a storage and control circuit which includes a memory, in which the volume signal corresponding to the volume which has been set can be stored, when the manual volume-setting device (14) is switched on, following a detection signal for a desired vehicle speed.
In accordance with the invention, therefore, the volume of the motor vehicle radio can be set automatically or manually, as desired, where, when the volume is set manually, the volume which has been set can be stored as a simple detection signal, together with the associated speed, so that this speed/volume signal pair then can be used subsequently for the automatic volume control.
By this means it is possible to build the motor vehicle radio of the invention into any motor vehicle which is equipped with a speed sensor, and any user can then adapt the automatic volume control device individually to his needs. Thus each driver can simply preprogram his individual sound volume, which is then set automatically as a function of the speed at which the vehicle is traveling at any moment.
In a first example of an embodiment of the invention, it is provided that the volume signal of the manual volume-setting device can be applied to the automatic volume control device by means of a momentary-contact switch. In this way, an especially simple operation of the motor vehicle radio of the invention is achieved, Wherein the speed-dependent adjustment of the automatic volume control device by the driver practically does not distract him from traffic.
In another development of the invention, it is provided that the volume signal of the manual volume-setting device can be applied to the storage and control circuit of the automatic volume control device through an analog-to-digital converter. This makes it possible to use the voltage signal which is to be applied to an output stage of the radio as a volume signal corresponding to the volume which has been set.
In order to further simplify the circuitry of the motor vehicle radio in accordance with the invention, it is also provided that the digitalized volume signal applied to the storage and control circuit serves as the detection signal.
A further example of an embodiment of the invention is distinguished by the fact that the volume signal supplied by the storage and control circuit as a function of the speed signal is applied through a digital-to-analog converter to the two-position switch as a voltage signal.
In order to construct the automatic volume control device of the motor vehicle radio in accordance with the invention in as flexible a manner as possible, it is provided, in a preferred embodiment of the invention, that the memory of the storage and control circuit is a write/read memory, the content of whose memory can be overwritten. In particular this makes it possible for various users of a motor vehicle to adapt the automatic volume control device individually to their hearing and to the prevailing weather conditions which affect the outside noise in any particular case.